The present invention relates to a double-seat valve unit with a leakage control. More particularly, it relates to a double-seat valve unit which has two independently movable valve plates of which one valve plate abuts against the other valve plate during opening after a predetermined stroke so as to form an inner chamber from which a leakage conduit leads to open air.
With the increasing automatization of the beverage industry, the requirements are made to provide for an automatic cleaning of the flow path of the product. In connection with this, program controlled chemical cleaning processes are proposed which allow remote control of cleaning operations. Valves are proposed which can be utilized for the thus produced and exactly determine working operations. When such valves are utilized, for example, in tank batteries, the individual working steps such as filling, emptying, cleaning and disinfecting must be performed in a simple way. Because of the strict safety requirements, an unobjectionable separation of the product from the cleaning fluid is necessary. For this reason, valves with two valve plates are utilized, particularly in the beverage industry. The valve plates which move relative to one another form an inner chamber which communicates with a leakage fluid conduit having a free end spaced from the valve seats and leading to open air. In such a construction, insufficient tightness of the valve can be fast recognized by an outwardly flowing leakage fluid and eliminated before inflicting further damages. In order to make easier dismounting in the event of some failures, the greater valve plate is located in the known constructions in the upper region. The smaller valve plate is located under the greater valve plate and moves from below upwardly to an opening position. In this operation the adjustment arrangement is actuated, and then the lower smaller valve plate first after a small partial stroke moves to abut against the greater valve plate, and thereupon both valve plates are removed from their seats. Such construction is discloased, for example, in the German Auslegeschrift No. 2,532,838.
The above-described double-seat valve unit possesses, however, a considerable disadvantage. This disadvantage resides in the fact that a portion of the leakage fluid conduit which extends outwardly of the housing moves during a switching step into the housing. Thereby an infection of the medium accommodated inside the housing by bacteria deposited on the shaft of the leakage fluid conduit is not excluded.
Moreover, the location of the smaller valve plate below the greater valve plate, particularly in condition of unavoidable back strokes in the lower housing region, causes the danger that both valve plates are shortly lifted from their seats and thereby mixing of the media which must be separated from one another can take place.